Translation

Overview of Translation in Protein Synthesis

  • Purpose: mRNA is decoded by ribosomes to synthesize proteins.

  • Location: occurs in the cytoplasm of the cell.

Key Terminology

  • Ribosomes: The protein synthesis machinery in cells, consisting of a large and a small subunit.

    • Size of Prokaryotic Ribosomes: Approximately 70S, composed of:

    • Large Subunit: 50S

    • Small Subunit: 30S

Stages of Translation

Step 1: Initiation

  • Process:

    • The small ribosomal subunit binds to the mRNA near the start codon.

    • tRNA carrying fmet (AUG) pairs w/ anticodon UAC w/ start codon

    • Initiation factors help position everything correctly

    • The large ribosomal subunit joins the complex

    • tRNA enters P site of ribosome

Step 2: Elongation

  • Process:

    • Another tRNA enters the ribosome.

    • The ribosome moves one codon down the mRNA in the 5'-3' direction.

    • tRNA shifts A > P > E

    • A site opens for the next tRNA

    • The tRNA in the E site leaves, leaving the amino acid

    • Pattern continues to grow AA chain

Step 3: Termination

  • Process:

    • The process of termination occurs when the ribosome reaches a stop codon on the mRNA.

    • Release factors bind to the stop codon in the A site, these proteins free proteins (new AA chain) and split ribosomal subunits

    • released polypeptide folds into 3D structure

Summary of Key Points

  • The translation process is critical for protein synthesis, facilitated by the ribosomes in the cytoplasm.

  • Each of the steps of initiation, elongation, and termination play a vital role in ensuring that proteins are synthesized accurately and efficiently.

  • The correct pairing of tRNA with the mRNA codon is essential for adding the correct amino acids to the growing polypeptide chain, ultimately folding into its functional three-dimensional structure.

  • Example of Codon Recognition:

    • Start codon AUG pairs with tRNA UAC carrying methionine.

  • Elongation Example:

    • As tRNA enters the ribosome, an amino acid pattern continues to grow, illustrating the dynamic nature of polypeptide synthesis during the elongation phase.